Cell-Free Supernatants of Plant Growth-Promoting Bacteria: A Review of Their Use as Biostimulant and Microbial Biocontrol Agents in Sustainable Agriculture

Marika Pellegrini, Giancarlo Pagnani, Matteo Bernardi, Alessandro Mattedi, Daniela M. Spera and Maddalena Del Gallo
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Marika Pellegrini: Department of Life, Health and Environmental Sciences, University of L’Aquila, Coppito, 67100 L’Aquila, Italy
Giancarlo Pagnani: Faculty of Bioscience and Technologies for Food, Agriculture and Environment, University of Teramo, Campus Universitario di Coste Sant’Agostino, 64100 Teramo, Italy
Matteo Bernardi: Department of Life, Health and Environmental Sciences, University of L’Aquila, Coppito, 67100 L’Aquila, Italy
Alessandro Mattedi: Department of Life, Health and Environmental Sciences, University of L’Aquila, Coppito, 67100 L’Aquila, Italy
Daniela M. Spera: Department of Life, Health and Environmental Sciences, University of L’Aquila, Coppito, 67100 L’Aquila, Italy
Maddalena Del Gallo: Department of Life, Health and Environmental Sciences, University of L’Aquila, Coppito, 67100 L’Aquila, Italy

Sustainability, 2020, vol. 12, issue 23, 1-22

Abstract: Plant growth-promoting bacteria (PGPB) afford plants several advantages (i.e., improvement of nutrient acquisition, growth, and development; induction of abiotic and biotic stress tolerance). Numerous PGPB strains have been isolated and studied over the years. However, only a few of them are available on the market, mainly due to the failed bacterial survival within the formulations and after application inside agroecosystems. PGPB strains with these challenging limitations can be used for the formulation of cell-free supernatants (CFSs), broth cultures processed through several mechanical and physical processes for cell removal. In the scientific literature there are diverse reviews and updates on PGPB in agriculture. However, no review deals with CFSs and the CFS metabolites obtainable by PGPB. The main objective of this review is to provide useful information for future research on CFSs as biostimulant and biocontrol agents in sustainable agriculture. Studies on CFS agricultural applications, both for biostimulant and biocontrol applications, have been reviewed, presenting limitations and advantages. Among the 109 articles selected and examined, the Bacillus genus seems to be the most promising due to the numerous articles that support its biostimulant and biocontrol potentialities. The present review underlines that research about this topic needs to be encouraged; evidence so far obtained has demonstrated that PGPB could be a valid source of secondary metabolites useful in sustainable agriculture.

Keywords: plant growth-promoting bacteria; cell-free supernatants; cell-free metabolites; spent cultures; exopolymers; biofertilization; phytopathogenic microorganism inhibition (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2020
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